RectControl, by Adam Sacks, gives control over rectangles in After Effects. It is designed for UI and SaaS animation and useful for more. Core controls cover alignment, corner roundness (linked or separate), corner curvature (convex versus concave), and a squircle option for Apple-style panels.
Much of the tool centres on pinning. You can dynamically pin elements inside or outside your rectangle, and pin gradient stroke and gradient fill start and end points to it. Shapes animate through the Effects Controls, and projects can be passed to animators who do not have RectControl installed, who can still use the Effect Controls. Adding pinned nulls or adjusting alignment without changing position does require RectControl installed. Beyond rectangles, it can change layer anchor points without changing layer position, add parent or child nulls, and use a 9-point grid on non-RectControl layers.
The Extensions panel lets you create RectControl layers, change alignment, create nulls, and save default and preset rectangles. Regular rectangles and Figma rectangles can be replaced with RectControl versions. It supports After Effects 2020 through 2026.